The present invention relates to a multiplex communication system for a vehicle, and more particularly to a multiplex communication system for a vehicle in which a large number of loads mounted on the vehicle are integrated into a plurality of units which are multiplexed for saving lines between the units.
Generally, in a vehicle, loads such as various kinds of lamps and motors are arranged dispersedly in parts of the vehicle, operation switches for operating the loads are disposed in the vicinity of a driver's seat, and the operation switches and the loads corresponding thereto are interconnected to each other by signal lines. Since recent vehicles mount a large number of loads, the number of signal lines increases and the diameter and weight of a wire harness (WH) bundling the signal and power lines also become large; work for wiring the wire harness in the vehicle becomes extremely burdensome and the vehicle weight also increases.
A conventional multiplex communication system has been proposed in that the operation switches disposed in the vicinity of a driver's seat are integrated into a single switch unit close to the driver's seat. Further, the loads arranged dispersedly in the parts of the vehicle are divided into front and rear groups of the vehicle in which each load of the two groups is integrated into a load drive unit arranged on the vehicle floor corresponding to the respective groups. In addition, the load drive units are interconnected by a multiplex line. With the proposed conventional system, a communication between the units can be made via the multiplex line for operating the corresponding load in response to an input signal from a specific operation switch, so that the number of lines of the wire harness which must be wired for connecting the operation switches and loads is drastically reduced.
The loads integrated into each load drive unit are connected to each other by the power and signal lines. On the other hand, with the proposed system, the loads are grouped on the front and rear of the vehicle and both the load drive units for integrating and connecting the grouped loads are arranged on the vehicle floor.
Thus, particularly in a bus vehicle arranging a large number of illuminating lamps and the like on the ceiling, the number of lines of a wire harness bundling power and signal lines increases and becomes bulky for connecting a large number of loads disposed on the front and rear of the ceiling to each load drive unit. In addition, the wire harness must be wired between the ceiling and floor.
However, a place for wiring the wire harness between the ceiling and floor is limited to specific places such as the wall faces of the vehicle; particularly the bus has a structure with the vehicle wall faces formed with a large number of glass windows, so that it is difficult to form the wire harness wired between the ceiling loads divided on the front and rear of the vehicle and the units disposed on the vehicle floor with high assembling performance or productivity.